The present invention concerns electrochemical preparation of diaryliodonium salts in a single or undivided electrolytic compartment or cell.
The electrochemical formation of diaryliodonium salts is known for benzene with iodobenzene (see Wendt: H. Hoffelner, H. W. Lorch, H. Wendt, Journal of Electroanalytical Chemistry, 66 (1975), pp. 183-194) and toluene with iodobenzene (see Miller: Larry L. Miller, A. K. Hoffman, JACS, 89 (1967), pp. 593-597) using platinum electrodes, divided cells, acetonitrile solvent and perchlorate electrolyte. In both cases, these do not represent commercially feasible sets of conditions. Divided cells are more expensive to operate due to additional voltage drop in the cell. Platinum is too expensive for anode material on a commercial scale. Furthermore, the electrodes of these systems are prone to coating by reaction by-products, thereby inhibiting their effectiveness.
Other prior art of interest includes U.S. Pat. No. 4,759,833 which discloses the simultaneous preparation of a diaryliodonium salt and an alkoxide salt using a divided cell. The only anode taught in this patent is platinum.
Diaryliodonium salts have a variety of uses, such as photoinitiators (U.S. Pat. Nos. 4,136,102 and 3,981,897), fungicides (U.S. Pat. Nos. 3,944,498 and 3,763,187) and bactericides (U.S. Pat. Nos. 3,885,036 and 3,712,920). Thus, it would be desirable to have a more economically and industrially feasible process for preparing such compounds, as well as for preserving the effectiveness of the electrodes. A new electrochemical method for synthesizing diaryl iodonium compounds has been developed and patented by Cushman, et. al. (U.S. Pat. No. 5,277,767), which is less costly and able to compete effectively with the traditional methods.
The present invention is directed to an electrolytic process for the preparation of a compound including the steps of: (1) charging an electrolytic cell fitted with at least one anode and at least one cathode in a single compartment with a reaction mixture, (2) applying electric potential to the anode and the cathode under conditions to promote formation of a compound on one of the cathodes or one of the anodes to define a formation electrode, and (3) agitating the formation electrode to facilitate the removal of the compound.